Comment by Laremere

If you look at the first place (after clear cheaters) time trials for different tracks, you'll see different choices but clear patterns. The main mode of the game has you race a set of four different tracks, and the online mode throws in all of the tracks; So in those modes the choices are going to be more constrained towards an average good.

For my part, I got the best rank in single player on all pre-DLC tracks with only toad and the default kart, so it's a part of the game you can entirely ignore if you're not competing against other humans.